A conventional exercise bike includes a main frame which is generally fixed, so it only provides the function of bike riding, not having the function for the user to stretch his/her body. Taiwan Patent Application No. 95200757 discloses “an improvement of an exercise bike”, and Taiwan Patent Application No. 94221425 discloses a “horse riding exercise bike”. When these two exercise bikes are used, the handle and the seat can be synchronously swung back and forth along with the motion of the pedals. But, the handle and the seat are always maintained in an equidistant state. Only the user's body shakes back and forth. It cannot achieve the function of full-body exercise. In addition, the fixed exercise bike is bulky and cannot be folded, so it always occupies space. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.